The present invention relates generally to tillage tools and, more specifically, to a knock-on or fastenerless sweep with structure for preventing a sweep from falling off the end of a shank.
Standard assemblies for implements such as chisel plows and field cultivators typically include a spring trip shank assembly extending downwardly to a tool-receiving end which mounts a shovel, point or sweep. Previously available mounting structure included bolts extending through holes in the tool and the shank to secure the tool. When the tool in such an assembly has to be replaced because of wear or damage, the bolts must be removed. Wear and corrosion of the bolts substantially hinders removal and often makes the replacement a difficult and time-consuming task.
Several solutions to the problem of easily and quickly replacing worn elements such as sweeps on shanks have been developed over the years, including adapter brackets providing a self-locking fit with a matching taper on knock-on sweeps, and frangible pins. Most retaining devices have suffered from one or more problems, including need for additional parts and the loss of sweeps when encountering high removal forces during transport and during rebounding of the shank from a tripped position. To reduce incidences of sweeps falling off the shanks in quick mount arrangements, some manufacturers have offered detent mechanisms such as a retaining clip in the form of a sheet metal stamping with a spherical protrusion that fits into a hole in the sweep. To release the sweep, a screwdriver or other tool is used to depress the clip and move the protrusion away from the hole. Other detent arrangements are shown, for example, in U.S. Pat. Nos. 3,061,021 and 6,289,996. Such detents generally help retain the sweeps on the shanks, but the forces exerted on a sweep, particularly forces exerted on deep tillage tools, can be so great that the sweep fails to stay on the shank. The geometry of most previously available sweep detent arrangements, including non-symmetrical mating surfaces on some, usually limits penetration of the retaining surface into the hole so that retaining forces are limited. Some care must be taken to align the protrusion with the hole, and part tolerances, variations in force used to mount the sweep, or lack of indexing of the clip relative to the shank can make such alignment troublesome. A relatively small, ramped contact area between the clip and the hole also increases the potential for losing a sweep. Soil moving up and around the stem portion of the sweep can move the clip from the detent position or wear away the clip until it is ineffective for holding the sweep on the shank. Extreme forces on the detent, such as those which occur during rebound, can also cause deformation of the detent. If the detent deforms, loosened sweeps can unacceptably dangle from the shank or be lost. A hefty detent construction or frequent detent replacements are therefore usually required.
In copending and commonly assigned U.S. application entitled KNOCK-ON SWEEP STRUCTURE AND TOOLS THEREFOR, Ser. No. 09/982,901, filed Oct. 19 2001, a sweep assembly is described having a retainer fabricated from wire spring material and supported in a groove on the underside of the wedge support which mates with stem portion of the sweep. The end of the wire is biased toward a contact area on the top edge of a slot in the stem to prevent the sweep from slipping down away from the wedged mounted position. To remove the sweep, a tool is inserted through the slot to depress the retainer end, and the sweep is forced downwardly off the wedge support. A common problem with sweep detents is most have a fixed detent position, and manufacturing tolerances in the sweep and support can result in an overly loose or tight fit at the detent position. If there is excess looseness in the fit between the sweep and sweep adapter, the detent structure may have to bear substantially all the retaining load. If the fit is too tight, the sweep may never reach the detent position and may be lost during transport or at the end of a shank rebound. Providing the manufacturing tolerances necessary for proper alignment can make the cost of the device prohibitive. Often the operator must apply a very large driving force to the sweep with a hammer or other tool to provide the wedge lock or assure that the sweep reaches the detent position.
It is therefore an object of the present invention to provide an improved sweep retaining structure for a knock-on sweep that overcomes one or more of the above-mentioned problems. It is another object to provide such an improved sweep retaining structure which is simple and inexpensive to manufacture and assemble and yet reliably holds the sweep on the shank and facilitates quick and easy attachment and removal of the sweep.
It is yet another object to provide an improved sweep retaining structure which provides reliable retention independently of manufacturing tolerances. It is a further object to provide such a structure having simplified and more reliable sweep attachment which requires less mounting force when initially attaching a sweep so the sweep can be attached by hand.
It is another object to provide an improved knock-on sweep for use with a sweep retainer. It is a further object to provide such a sweep having improved mating structure for a better fit with the retainer, even if there are relatively large manufacturing tolerances in the sweep mounting structures.
Sweep retaining structure includes a retainer having a contact end biased towards the sweep. The sweep includes two or more spaced retainer-receiving areas to accommodate manufacturing tolerances and facilitate hand mounting. In one embodiment, the retainer is a wire made of spring steel having a contact end biased against the underside of the sweep. The underside of the sweep includes a series of stepped portions or to provide a ratcheting function. As the sweep is slid onto the adapter on the shank, the contact end springs into a first retaining position on the stepped portion that aligns with the spring end. The first position maintains the sweep on the shank without need to forcibly drive the sweep onto the adaptor, and the attachment can be done by hand without tools. The force applied to the sweep during initiation of normal operation moves the sweep into a wedge locked position and provides a self-ratcheting effect for the retainer structure. If tolerances are such that the sweep moves upwardly on the shank beyond a central position, a stepped portion closer to the tip end of the sweep is engaged by the end. If tolerances provide a tighter fit so that the sweep does not move as far up the shank, a stepped portion closer to the upper end of the sweep is engaged.
To remove the sweep, a tool is used to engage and depress the retainer. In one embodiment, the tool fits behind the stem of the sweep so that a slot in the sweep adjacent the retainer is obviated for improved retainer operation and increased retainer life. The parts can be reversed in an alternate embodiment so that the stepped portions are on the shank or wedge adaptor and the retainer is on the sweep.